Yesterday my e30 started generating a persistant CEL (Check Engine Light) error 1221 which indicates the o2 sensor has failed or is sensing values so far out of spec it can’t be interpretted. I suspect that driving around with a nagging misfire for almost a month fouled the sensor. The sensor is only a couple months old, which is a shame. Thankfully I kept my old sensor which I’ll use until it fails or I finally swap in a s52 engine.
The happy ending to this is that it’s finally fixed! But I’m going to relate the story in 3 sections: what I’ve learned, what fixed the problem, and then I’ll talk about everything else I tried to fix the problem.
So I’ve heard of the CPS before. Heard people talk about:
Generally I was confused and unsure of what to do with it, though I knew it was in scope for the problem I was having. Here’s the layman’s explanation of what the CPS does (source):
Any one of the things I’ve replaced could cause the symptoms I’ve noted, but replacing parts did nothing because the parts weren’t actually failing or bad. Other things that were blamed by people I asked:
Most people want to throw parts at this kind of problem, so I’m glad it didn’t come to that for me. That’s the end of the story, so here’s some photos taken during the various fixes:
I got my pump and sender from the Pick n’ Pull for $70. Normally I would not have installed used parts in this application but I found a remarkable specimen and scooped it. If you have the means I suggest buying new for reliability and because there are so many after-market pumps available that are excellent and cheap especially if you have an engine with a higher than average LPH (litres per hour) requirement.
In my photo above you can see the new pump and sender have nice white plastic bits while my old parts are all brown. This isn’t aging it indicates a material update seen in newer fuel pumps. Expect to spend $250-280 for a new pump and sender, less if you retrofit a non-OEM pump.
This job is dead simple and well documented. This thread on r3vlimited has some insights into noises and rusty fuel tanks. I won’t duplicate the step by step but I will share my notes on the procedure:
My e30 is messed up, stuttering and lacking power. Though it ran strong for an afternoon my “exceptional specimen” didn’t have much life left. Here’s how I’ve determined that the pump fuel supply is the problem: When the car stutters during acceleration, check the tachometer and fuel economy guages. If the RPMs drop that usually indicates a lack of spark. If the fuel economy drops that indicates the engine is starving for fuel.
My car is doing the latter, puttering at between 5 and 0 MPG in every gear and whenever the throttle is open. Tomorrow I’ll get up early and try hopefully swap in my old pump.
The old pump improved drivability but I can tell it’s a short term fix because my old pump is making noise sometimes and the MPG frequently and nearly bottoms out just driving normally. This could be a combination of factors (fuel pump, fuel pressure regulator, injectors) but I suspect the pump.
This time it only took me 15 minutes to swap pumps but I’ll be doing it again soon so maybe I can do it even faster next time. There are several aftermarket pumps available but I decided on an OEM pump from TurnerMotorsport (they have the best price).
The bodger retrofit is to buy a pump and kit and rig it into the pump armature. The most common pump for that applicaiton is the Walbro 255 GSS-340 (DIY Retrofit Instructions). Cars with higher displacement engines or turbos sometimes put in a pump with greater LPH (litres per hour) such as the Deatschwerks 300 LPH but that’s not necessary for a stock engine, even an s52 let alone an m20.
I’m a sucker for OEM.
I’m still convinced I have a fuel issue but my mechanic drove the car and says it has the tell-tale signs of a spark issue. I replaced the plugs in the 4 troublesome cylinders (which were actually o.k), replaced a cracked HT wire and swapped in the new distributor cap and rotor from my trunk kit for good measure: problem persists. If my mechanic is correct then the next item to inspect is the ignition coil.
My new OEM fuel pump arrived last night and I installed it in the dark. Works great and I can definitely feel that the car has new energy. Afterwards I drove it around the block with the pump exposed and the seat cushion off and it was crazy how loud the pump is. However my surging and powerloss issues prevail and I am going to replace the ignition coil to try to remedy that. As I’ve read, the coil can fail completely but it can also fail slowly causing exactly the symptoms I’m experiencing.
One last thing, It’s worth noting that every time I’ve done this there has been very little fuel in the hose coming off the pump, but this time there was much, much more fuel. It’s a good idea to remove the fuel sender before disconnecting the hose so you have somewhere to drain all that fuel.
Suction Device with Pre-Supply Pump (255 LPH) 16141179415
Sending Unit Assembly 16141152266
Got the car back today and it’s working fine. Would have loved to do the work myself but I don’t have the facilities nad it’s probably for the better as it’s a messy job. The following diagram isn’t of an e30 but it does explain how the master cylinder and slave cylinder are connected:
Here are the parts from the BMW service diagrams:
Oh yeah almost forgot about AAA. So they towed my car to the shop but because the e30’s oil pan is right over the front axles their truck scraped up my pristine oil pan. Kinda cheesed about it, but I guess it’s not that big a deal.
Car has been acting poorly for the last two weeks. Usually it stalls dead once on cold start. Then sometimes it hunts until it warms up, rarely it surges to 2.5K then settles at 1K and stays there but mostly it just bogs around 500 RPM until warm. If I leave the car off for 20-30 minutes it does bog but recovers faster. Considering the state of my spark plugs I suspect clogged injectors but I’d like to rule out a new vacuum leak first since this is classic vacuum leak behavior.
Recorded today after it stalled once on cold start, then did this:
The e30 developed a misfire on the final leg of our Sunday tour. It’s fixed now.
My mechanic says based on the buildup that the problem was plug #5 and the miniscule amount that the #1 HT wire was out by would have no effect. I’m not 100% sure with that diagnosis but the car is running and I’m happy. I will sand blast my old plugs and save them for spares as I will need to replace #5 in 3,000 miles. Or less.
His sound advice is not to put any more money into this m20 engine, which could run for a long time in it’s current state. And save for an engine swap, specifically a 3.2L e36 M3 motor a.k.a S52. If I get lucky I may get the engine for $2K, but install will be a whole other matter. If I do an engine swap then I may paint the engine bay at the same time.
e30 M20 Spark Plugs: NGK ZGR5A or Bosch Super Plus WR8LC+
Spark Plug Socket Size: 21mm
Spark Plug Torque: 15 – 22 ft. lbs.
For reference, diagnosing a misfire includes (but is not limited to) the following systems / parts:
Picked up and installed some used sidemarker sockets and new bulbs (part number 63217160797). All but one of the car’s sidemarkers has been disconnected and burned out since I got the car. Some day I’d like to put clear lenses (read: make) in my markers and front turn signals but that will have to wait.
On that note, here’s a few of my non-mechanics rules to buying a used e30:
I booked the vehicle bay at Tech Shop so that I could learn to jack up my car. I’ve jacked up other cars just to change a flat but never put a car up on stands. It was a good learning experience and a chance to take a look at the under carriage. Tech Shop had 2 floor jacks but only one was short enough to fit under the front support. Here’s the diagram I used to determine where to put the floor jack and stands:
Didn’t want to but no choice but to put the floor jack under the rear differential because my muffler was blocking the optimal spot on the subframe support. While I was under there I had intended on installing the heat shield I pulled 2 weeks ago but I couldn’t figure out how to get the muffler out of the way and ran out of time (the previous guy who booked the vehicle bay held me up for almost an hour which is a big faux pas at the Tech Shop). I may try again later.
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